1. Field of the Invention
The present invention relates to a pressure vessel formed by joining two members made of different materials. The pressure vessel can be suitably used, for example when a cylindrical member formed with a diaphragm is joined with another member so as to constitute a pressure vessel, in a pressure sensor element, which detects a pressure of a fluid by using a diaphragm.
2. Description of the Related Art
It has been widely known to effect plastic deformation joining of two members made of a metal and a non-metal respectively, or two metals, by causing one member made of metal to undergo plastic deformation locally for fitting into the joining groove provided in the other member (refer to JP 61-042444 A, for example).
JP 61-042444 A discloses a method of joining a clutch cone and a transmission gear. Circular grooves for effecting the plastic deformation joining are formed in an inner peripheral surface of a clutch cone. After the clutch cone is press fitted into the transmission gear, a second punch is press fitted into a position in the vicinity of the joining face of the transmission gear. A portion of the transmission gear is plastically deformed toward the clutch cone to join the transmission gear and the clutch cone together.
Further, though not described in the specification of JP 61-042444 A, FIGS. 1 to 6 of JP 61-042444 A show a joggled face provided in the transmission gear, by use of which positioning in an axial direction is performed when the clutch cone is press fitted into the transmission gear.
Further, JP 09-318480 A discloses a pressure sensor in which a cylindrical component formed with a diaphragm is hermetically held in a pressure vessel by means of an O ring mounted to the cylindrical component.
According to the joining method of metallic members disclosed in JP 61-042444 A described above, the plastic deformation is sufficiently effected with a small pressurizing force, and two metallic members are joined together with high joining strength and high precision. However, the joining method of metallic members disclosed in JP 61-042444 A mainly deals with joining in a rotational direction. It does not attach much importance to hermeticity between the two members.
On the other hand, in the pressure sensor disclosed in JP 09-318480 A, hermeticity between the cylindrical component and the pressure vessel is taken into consideration, but it does not deal with joining of two members by plastic deformation.
In general, pressure sensors themselves are used for a variety of purposes. It is preferable that they can withstand the uses under any environment, and they must be strong against changes over time. Considering the above, the O ring is not necessarily the ideal solution.
Meanwhile, welding by irradiation with a laser beam is known as a joining means for joining a diaphragm element to a mounting pedestal. SUS 630 is used for the diaphragm element as a pressure sensor, and SUS 430 is used for the mounting pedestal. Metallic glass has recently drawn attention as a material having a low Young's modulus and high breaking strength. When metallic glass is used for the diaphragm element, and the diaphragm element is joined with the mounting pedestal by welding through laser beam irradiation, the following problems arise: No matter how short the time for irradiation with the laser beam is, the welding portion reaches a melting temperature. The welding portion reaches the crystallization temperature of the metallic glass to crystallize the metallic glass. The diaphragm may deteriorate in its performance, or may be broken, which becomes an obstacle to practical application.
Furthermore, the pressure sensor needs to function as a pressure vessel as well. Needless to say, joining force between the members should be improved. If there is a leak of fluid from a fitting portion of the diaphragm including a joint portion due to an increase in pressure within the pressure sensor, this will become a problem. Accordingly, it is desirable in the pressure sensor that the joining force between members be improved, and hermeticity of the pressure sensor as a product be permanently kept within a passing range, at a leak rate of 9.9×10−10 atm·cc/sec. or less